Stored program controlled communication switching systems comprise some form of intelligence which controls switching functions in response to a program stored in memory. Historically, such systems included a single processing entity for the control of the entire system. As technology and system design evolved, it was desirable to separate certain routine functions from the main processing entity to save its processing time for more complex system functions and decisions. Today, systems are being designed which also separate some of the more complex system functions and decisions into several intelligent processors. Throughout the evolution of switching system control strategies, changes have occurred in the way the various processing entities intercommunicate. Some systems have provided a separate controller bus structure to be used for all communications among the processors. Other systems have utilized the communication paths of the switching system to provide communication paths between the distributed system processors and a central controller which interprets control information and directs the overall operation of the switching system. These known systems, however, require that complex and time consuming operations be performed in their implementation. Further such systems cannot take full advantage of distributed processing due to their reliance on a central controller to direct the distributed processors.
A control information communication arrangement in accordance with the invention of U.S. Pat. No. 4,322,843 of H. J. Beuscher et. al. issued Mar. 30, 1982, and assigned to the assignee of the present application, achieves the benefits of interprocessor communication while reducing the complexity and time consuming nature of previous arrangements. In accordance with one exemplary embodiment of the invention of the above-cited Beuscher patent, control units intercommunicate via certain switching system communication paths by means of control messages comprising a plurality of control words. A control distribution unit included in the switching system of the exemplary embodiment accumulates the control words of a control message being transmitted by one of the control units and, after the entire control message has been stored, the message is routed to the control unit defined by an address portion of the message when a communication path to that control unit becomes available. However, since the control distribution unit in the exemplary embodiment stores the entire control message, interprocessor communications can be significantly delayed when control messages comprise many control words. Further, since a given control unit may sequentially transmit a number of control messages, all of which must be stored in the control distribution unit of the exemplary embodiment because of the lack of available communication paths to destination control units, the magnitude of the storage facilities included in the control distribution unit must be large. Further, the possibility that transmitted control messages may be lost when the provided storage facilities are all being used to store other control messages complicates the fault recovery procedures that must be developed to assure high system reliability. In view of the foregoing, a recognized problem in the art is achieving the benefits of interprocessor communication using the communication paths of a switching system in accordance with the invention of the above-cited Beuscher patent without unnecessarily delaying the interprocessor communication and without the cost and complexity associated with the storage facilities of the above-described exemplary embodiment.